One of the problems with stacked semiconductor dies is a requirement for interconnection. Typically such interconnection is achieved by wirebonding, because techniques used for direct bondpad-to-leadframe connections, such as flip chip and bump connections, are difficult to achieve in the situation of multiple dies. In addition, if a multi-chip module (MCM) is to be pre-characterized and tested, dies which are inoperative must be disconnected and then re-connected to the package substrate. In addition, the transfer of data at high speeds creates problems with respect to lead wires, in that the lead wires tend to have significant inductance, particularly at high frequencies. Accordingly, it is desired to provide a multi-chip module (MCM) in which communication is effected in a manner which bypasses the requirement for lead wires.
Another problem with stacked dies is that, if it is desired to communicate between the dies, then some form of a connection must be made between the dies. There are two ways to accomplish this: 1) direct interconnection from one die to another die; and 2) connection from one die to a lead frame or a connection on a package substrate and a second connection from the lead frame or substrate to a second die. In the case of a direct connection, it becomes necessary to provide wirebonding from die to die. In the case of an interconnection through the lead frame or substrate, a double connection is required, thereby a creating a potential for more signal loss. Accordingly, it is desired to provide a signal communications system for semiconductors in which multiple semiconductors in a vertically spaced relationship or in a closely-spaced relationship are able to communicate. It is further desired to reduce the number of internal connections for a semiconductor package, and if possible, not greatly exceed the lead count for the package.